Polymerization process for unsaturated fluoroolefins



POLYMERIZATION PROCESS FOR UNSATURATED FLUOROOLEFINS Original Filed Dec. 15, 1954 c f z f 622/552 Pressure geit/fafa.

ATTORNEY United States Patent O 3,163,628 POLYMERIZATION PROCESS FR UNSATURATED FLUURULEFWS Archibald N. Bolstad, Afton, Minn., assigner, by rnesne assignments, to Minnesota Mining and Manufacturing Company, St. Paul, Minn., a corporation of Delaware Continuation of application Ser. No. 475,385, Dec. 15,

1954. This application Feb. 28, 1961, Ser. No. 92,388 7 Claims. (Cl. i60-87.5)

pressure at whichtbe monomer or monomers being pon lymerized condense at a specific temperature of reaction. In polymerization reactions, the pressure employed determines to a great extent the rate of polymerization, the temperature determines the dilute solution viscosity, or the molecular weight, of the polymeric product, and the monomer feed composition determines the composition of the polymeric product.

Heretofore, when polymerizing two or more monomers having dierent reactivities in the liquid phase or under autogenous conditions of pressure to produce a copolymer or terpolymer of a certain specific composition, it has been necessary to vfirst calculate the monomer reactivity ratios, to limit the conversion below a certain maximum percentage, and to use incremental feeding of monomers to obtain the desired results.

The process of the present invention, on the other hand, produces a copolymer or terpolymer having a composition practically identical with the feed composition, especially when the monomers are substantially in the vapor phase. Deviations which are sometimes encountered are possibly accounted for by undesirable side reactions. The monomer mixture to be fed into the polymerization or reaction zone, in one embodiment of the present invention, is prepared in a steel cylinder and is in the liquid phase. In order to insure that the -feed charged to the reaction zone is of a composition which will result in a copolymer or terpolymer having the desired composition, it lis sometimes necessary to add an estimated excess of one or more of the monomers to the mixture of monomers in the steel cylinder. This .excess vis to compensate for diiferm ences in volatility ofthe monomers. The vapor above the liquid monomer mixture in the vfeed tank will be richer in the more vola-tile monomer. An excess of one or more of the monomers is also desirable in some cases to compensate for the slight quantity of monomer or monomers consumed in side reactions. Usually a preliminary run will sutlice to provide the necessary information'to make an accurate estimate ofthe quantity of excess monomer or monomers which should be added to the monomer feed mixture.

The process ofthe invention produces homogeneous copolymers, terpolymers, and the like, and morereiicient use of monomers is obtained with conversions approaching 100 percent, if desired. The process is therefore highly economical as compared to the processes of the prior art.

The molecular weight, as determined by the dilute solution viscosity of the polymer product, can -be controlled by regulating the temperature of polymerization. The pressure also affects the molecular weight of .the product but only up to a certain maximum pressure, above which an increase in pressure has no etfect upon the molecular weight. Modiers such as chloroform and carbon tetrachloride are not necessary to control the molecular weight of the product, using the process of the present invention.

ICC

The constant pressure method of the invention is also easily adapted to continuous operation in equipment having no moving par-ts. A large safey factor is also involved, since homopolymerization of a single monomer or polymerization between two or more monomers is controlled so that there is never a large amount of monomer or monomers present in the reaction zone, whereby a sudden and uncontrollable reaction of large amounts of material is avoided. The safety of the opera-tion is linked to the control factor of the process, the temperature and pressure being easily regulated and maintained constant.

The polymers of the invention may be prepared in various monomer ratios, when more than one monomer is used, and by employing the various conventional polymerization recipes. The temperatures employed in the polymerization reaction may be between about 0 C. and C. with the preferred temperature range being between about 5 C. -to 50 C. The polymers ofthe invention are prepared using one of a number of free radical promoted polymerization systems. Peroxy-type polymerization promoters have *been found to b e suitable in initiating desired polymerization reactions and are used in suspension or emulsion polymerization systems.

Of the water suspension-type catalyst systems which may be used, the redox catalyst system is preferred, comprising an oxidant and a reductant. The oxidant in the water suspension-type recipe is preferably an inorganic persulfate, such as potassium persulfate, sodium persulfate, or ammonium persulfate. The reductant is preferably a bisulfite, such as potassium bisuliite, sodium bisulte, potassium metabisulite, or sodium metabisulfte. The oxidant in the suspension Aredox recipe comprises between about 0.1 and 5 parts by weight per 200 parts of water present and preferably comprises between about 0.5 and 2 parts by weight per 200 parts of water present. The reductant, such as sodium metabisulte, may comprise between about 0.05 and about 5.0 parts by weight per 200 parts by weight of water present and preferably comprises between about 0.1 and 2 parts by weight per 200 parts by weight of water present. A bulfer such as sodium tetraborate may lbe used, if desired, together with the oxidant and reductant.

Also about 0.01 to about 0.2 part by weight per 200 parts by weight of water present of a variable valence metal salt may be used. The variable valence metal salt is preferably an iron salt such as ferrous sulfate or ferrous nitrate, and it is used as an activator. When producing the polymers of the invention in the persulfate-bisuliite suspension system, it is preferable to operate Aat a temperature range of about 25 C. to about 60 C., but lower 'temperatures, i.e. between about 5 C. and 25 C., are desirably employed when a variable Valence metal salt is present in the polymerization system. Also, the reductant and/or the variable valence metal salt may be eliminated, if desired. Y

Alternatively, an emulsion catalyst system containing Water, soap and a peroxy compound may also be used. The different types of emulsion systems may be conveniently differentiated on the .basis of the catalyst system used to initiate the polymerization system. One type is that in which the polymerization is initiated using a redox catalyst system comprising between about 0.01 to about 1 part by weight .per 200 parts of water present of an organic oxidant and an activator solution. Exemplary of the organic oxidants which may be used in the emulsion catalyst system are cumene hydroperoxide,`diisopropylfben zene hydroperoxide, triisopropylbenzene hydroperoxide, methylcyclohexane hydroperoxide, tertiaryfbutyl perbenzoate, and tertiary-butyl hydroperoxide. A typical activator solution may consist of about 0.01 to 1.0 part by weight per 200 parts of water present of a variable valence metal salt such as ferrous sulfate, about-0.1 to 10 parts'by Patented Dec. 29., 1964 weight of sodium pyrophosphate, and about 0.1 to l parts by weight of a reducing sugar such as dextrose.

Another type of emulsion cata-lyst system is that which comprises about 0.05 to 5 parts by weight per 200 parts of water present of a persulfate as the oxidant, and which preferably comprises between about 0.1 and about 0.5 part by weight of any of the persulfates previously mentioned as being suitable for use in aqueous suspension systems.

The soap employed as the emulsifying agent in either the redox or persulfate emulsion catalyst systems is preferably a metal salt, such as the potassium or sodium salt, derived from saturated aliphatic acids, the optimum chain length of the acid being between about 14 and about 20 carbon atoms, or from polyuorocabboxylic acids or peruorochlorocarboxylic acids. The polyfluorocarboxylic acids which may be used are those disclosed in US. Patent No. 2,559,752, and the derivatives of the acids disclosed therein as being efcacious dispersing agents in polymerization reactions may also be employed in the process of the present invention. The perluorochlorocarboxylic acids which may be used in the process of the present invention are those disclosed in copending application Serial No. 463,073, led October 18, 1954, now US. Patent No. 2,874,152, as being useful as dispersing agents in polymerization reactions. The soap is generally present in a quantity between about 0.5 and about parts by weight per 200 parts of water present. The emulsion polymerization is desirably conducted under alkaline conditions, and the pH should be maintained between about 9 and 11 in order to prevent gelling of the soap. The pH may be adjusted, if desired, by the addition of suitable buffers..

The process of the invention may be operated at pressures in the range of atmospheric pressure to about 500 p.s..g., the pressure which is employed in any specific reaction being determined by the volatility of the monomer or monomers to be reacted. The reaction time may be in the range of about 0.1 to 72 hours.

Monomers which may be copolymerized according to the process of the present invention may be divided into the following groups, the division being made on the basis of the boiling points of the monomers. The maximum pressures given are those below which the monomers will be in the vapor phase at room temperature, i.e. 25" C., and above which the monomers will begin to condense, i.e. the saturation pressure. The minimum pressures given are those which are necessary to obtain substantial amounts of polymer product.

, Max. Pres- Group: Rela- Boiling Point of sure at Minimum tive Volatility Monomers Room Pressure Temp.

1..--- M0st -180 to -40 C 560 p.s..g... 50. 2 Less -40 to 10 C 75 p.s.i.g 25. 3 Least- -10 to R.T. (25 CJ-- 40 p.s.i.g Atmospheric.

ZA-tetraiuorobutadiene; 1,1,i2-trifluorobutadiene; 1,1,3- trifluorobutadiene; 1,1-diuorobutadiene; and, fluoroprene.`

The process also includes polymerization of two or more monomers at a constant pressure which is below the saturation pressure of at least one of the monomers but which is above .the vapor pressure of one of the monomers at a specific temperature of reaction. In this embodiment of the invention, the composition of the copolymer produced from a given feed mixture of 2 monomers will not be as close to `the composition of the feed as in the case where both monomers are copolymerized below their saturation pressures at a specific reaction temperature. However, in addition to the other advantages inherent in this invention, the copolymerization of monomers wherein the vapor of one of the monomers is in contact with a liquid comonomer, leads .to copolymers containing a higher mol percentage of the less reactive monomer, as compared with the amount which is incorporated in to the polymeric product when autogenous pressure is used. This advantage is particularly important when copolymerizing monomers such as CFFCFCI and OF2=CH2 with relatively reactive monomers such as chloroprene and styrene. Typical examples of monomers which are included within this embmodiment of the invention are those whose boiling points are above 25 C. at atmospheric pressure, such as styrene, phenyltriuoroethylene, vinylidene chloride, 2,3- dichlorohexailuorobutene-2, chloroprene, acrylonitrile, alpha-trifluoromethyl-acrylonitrile, butyl acrylate, vinyl carboxylates such as vinyl acetate, etc.; vinyl ethers such as vinyl ethyl ether, vinyl isobutyl ether and vinyl 2- chloroethyl ether; and fluoro-l-dienes and such as 1,1- dilluoro-2-methylbutadiene, l,l-dilluoro-S-methylabutadiene and 1,1,3-triiluoro-Z-methyl-butadiene.

Whenever conditions permit, it is preferable to colpolymerize both monomers below their saturation pressures with in the temperature ranges mentioned in the disclosure.

For example, vinylidene chloride, whose boiling point is 32 C., may be copolymerized while substantially in the vapor phase by employing slightly elevated temperatures at atmospheric pressure and/or by -using a feed containing a low concentration of vinylidene chloride.

The pressure ranges given in the above table for each group apply to the copolymerization of monomers within the same group, and when copolymerizing monomers of two different groups, revision of the maximum pressures given in the table above may be required. For example, a feed mixture consisting of any molar percentage combination of triuoroethylene and vinylidene uoride or tetrai'luoroethylene may be polymerized while in the vapor phase at room temperature at pressures up to 500 p.s..g. and preferably not higher than 300 p.s..g. to produce a copolymer having about the same composition as that of any specific feed used. When copolymerizing equimolar quantities of tritluoroethylene with chlorotrifluoroethylene or 1,1-chlorofluoroethylene, however, the polymerization pressure should not be in excess of 140 p.s..g. at 25 C., and when copolymerizing the monomers of a feed mixture consisting of 25 mol percent of trilluoroethylene and 75 mol percent of chlorotriuoroethylene or 1,1-chlorolluoroethylene, the polymerization pressure should not be in excess of p.s..g. From the foregoing, it will be seen that as the molar percentage in the feed of the less Volatile monomer is increased with respect to the molar percentage of the more volatile monomers, the maximum pressure will necessarily have to be decreased.

The process of the invention may be operated with the monomer or monomers being completely in the vapor phase, but it is desired at all times to maintain at least one of the monomers being polymerized substantially completely in the vapor phase. When polymerizing a mixture of two or more monomers, the pressure in the polymerization zone may be such that one monomer is substantially completely in the vapor phase and the other monomer may be substantially completely in the liquid phase. will be substantially completely in the vapor phase,

Generally, the monomer or monomers although an equilibrium always exists between the monomers in the vapor phase and the monomers in solution in the aqueous catalyst phase.

In one method of producing polymers according to the process of the invention, a polymerization bomb is charged with a catalyst solution, evacuated, and connected to a cylinder containing a monomer or mixture of monomers, the cylinder being connected to the bomb by means of a conduit having a needle valve therein. The feed is then introduced into the bomb through the needle valve at a controlled rate suiiicient to maintain the pressure of polymerization at a desired constant value. Agitation of the contents of the bomb is provided by rocking the system, and the bomb may be heated, if desired.

At the end of the polymerization period, the feed of the monomer or monomers to the bomb is discontinued, and the product is removed in the form of a latex which is then coagulated with an'electrolyte or by freezing. The' product is then Washed and dried to obtain the desirevd polymer product.

Referring to the accompanying drawings, one embodiment of an apparatus is shown which is useful for producing polymers, according to the process of the present invention, on a commercial scale. The apparatus consists of a vertically elongated vessel 2, which may be fabricated from any non-corrosive material such as stainless steel or the like, having a jacketd thereon. Any suitable heat exchange medium may be passed through the jacket for the purpose of controlling the temperature of polymerization within the vessel 2. A conduit 6 connects to a catalyst solution storage, not shown, and With a proportioning gear pump 8 which pumps the aqueous solution through the conduit 10, the valve l2, and the spray head 14 mounted in the top of the elongated vessel 2. The spray head uniformly distributes Ia ne spray of the aqueous catalyst solution downwardly through the elongated vessel or polymerization reactor, Where it contacts rising monomer vapor or vapors introduced through the conduit 16 and the pressure regulator 18 into the bottom of the elongated reaction vessel 2 from a monomer storage, not shown. The monomer or monomers are flashed as vapors from the pressure regulator 18 below the foraminous plate 2t) mounted in the bottom of the vessel 2, they plate uniformly distributing the monomer vapors throughout the cylindrical reaction vessel 2. A conduit 22 connects the Vapor space, or upper portion of the reaction vessel 2, with the suction side of a recirculating compressor 24 and a conduit 26 is connected to the discharge side of the recirculating compressor, terminating at a point 28 below the foraminous plate 20. A conduit 30 having a valve 32 therein is provided for withdrawal of polymer latex product from the bottom of the vertically elongated reaction vessel 2.

If desired, the tower 2 may be packed with any conventional packing such as broken stone, clay spheres, Carborundum, glass rings, porcelain saddles, porcelain rings',- and the like.

In" the operation of this apparatus, the reaction vessel 2 is brought to the desired temperature by means of a heat transfer medium circulating through the jacket 4, and an aqueous catalyst solution is introduced through the spray head 14 by means of the gear ptunp 8. As the spray of aqueous catalyst system descends through the reaction vessel 2, it is met by an upowing stream of monomer or monomers introduced through the conduit 16, the pressure regulator i8, and the dispersing foraminous plate 2'0. As the aqueous catalyst solution collects in the bottom of the vessel 2, the level of the liquid rises until the forarninous plate 20 is covered, and additional catalyst may be introduced continuously or intermittent- 1y. The monomers are introduced at a rate sufficient to maintain the pressure within the vessel constant, and monomers from the vapor space are recirculated through the conduit 22, the recirculating compressor 24, and the conduit 26 in order to maintain the monomer system at a 6 constant composition. As the latex polymer product forms, it may be Withdrawn from the system through the conduit 30 and valve 32 at the bottom of the reaction vessel.

Thus, by correlating the feed of catalyst solution, the feed of monomer or monomers, and the withdrawal of the polymer product, the reaction may be operated continuously in the apparatus shown with sucient monomer o'r monomers being added at Iall times to maintain the pressure within the reactor 2 constant and by adding suiiicient catalyst, preferably continuously, to make up for that lost in the withdrawal of the polymer latex product. The pressure within the vessel 2 is maintained at all times below the saturation pressure of atleast one of the monomers being polymerized so that at least one of the monomers exists substantially completely in the vapor phase, although the monomer is beingl recirculated through the aqueous catalyst solution and some monomer is dissolved therein at all times.

This type of tower produces many advantages, since no moving parts are involved, and a better contact between the catalyst solution and the monomer or monomer mixture is obtained. Hazards are also reduced due to the fact that the quantity of monomer or monomers present in the polymerization zone is small at all times. Also, low operating pressures may be used, for example, pressures in the range of atmospheric to 1,50 p.s.i.g.

The invention will be further illustrated by `reference to the following specie examples in which all parts are by weight:

EXAMPLE 1 Preparation of Copolymer Containing 50 Mol Percent of Each of 1,1-Chl0r0fln0r0ethylene and T etmj'uoroethylene Employing the Constant Pressure Technique The following emulsion redox polymerization system was used:

Parts by Weight Water, deionized 200.0 Potassium persulfate 1.0 Sodium metabisulite 0.4 Ferrous sulfate 0.1 Peruorooctanoic acid 1.0

A stainless steel polymerization bomb was charged with the following catalyst solutions, freezing the contents in a solid carbon dioxide-acetone bath after each' addition:V

( l) l5() partsV of Water containing 1 part of dissolved peruorooctanoic acid,

(2) 30 parts of water containing 1 part of dissolved potassium persulfate,

(3) 10 parts of Water containing 0.1 part of ferrous sul.

fate heptahydr-ate, and

(4) l0 parts of water containing 0.4 pant of sodiumV was opened and the feed was introduced into` the bombV in the gaseous phase at a rate suficient to maintain the pressure of polymerization at 50 p.s.i.g. The entire system was rocked at ambient temperature which was about 25 C. At the end of 21 hours, 50 parts of feed-hadl been introduced into the bomb and the polymerization Was then stopped. The product in the bomb was in the form of a white latex. The latex was coagulated with a hot dilute sulfuric acid-sodium chloride solution. The coagulated product was collected, thoroughly washed with warm and cold water, and dried to constant weight in vacuo at a temperature of 35 C. A rubbery polymeric product was obtained in 90 percent conversion, and was found heterogeneity and powdery nature of this product is ac-v counted for by the fact that as the relative concentration to contain 20.1 percent chlorine, or 50 mol percent of 5 of the less reactive monomer, CF2=CF2, to the more combined 1,1-chlorouoroethylene and 50 mol percent of reactive monomer, CHzzCFCl, increases, the CF2=CF2 combined tetrauoroethylene. is drawn into the reaction to a greater extent. Therefore, The above procedure was repeated with the exception the resulting polymer possessed a preponderance of the that the feed, containing 50 mol percent of 1,1-chlorotetraiiuoroethylene monomer unit iat either end of the uoroethylene and 50 mol percent of tetrailuoroethylene, 1@ polymer chain, the product thereby assuming the powdery was introduced into the polymerization bomb at a rate nature of polytetraiiuoroethylene. This unevenness of sufficient to maintain the polymerization pressure between reaction of the two monomers produced the excessive 75 and 100 p.s.i.g. After 6.2 hours of polymerization at l spread of monomer ratios found in the copolymers listed a temperature of 25 C., the polymerization was stopped. in Table 1 above. The use of constant pressure or feed- The latex was dried in the same manner `as that set forth ing the monomers into the reaction zone in the vapor above and a rubbery product was obtained having apphase and maintaining the polymerization pressure below proximately the same composition as that of the polymer that which causes condensation of the monomers does produced above. not necessitate the calculation, based on reactivity ratios, EXAMPLE 2 of a specic molar charge to obtain a product of desired Preparation of a Copolymer of 1,I-Chlorofinoroetlzylcne Composltion' and Tetranoroethylene Under Autogenons Condz'lions A150 m Order to produce a mole homogeneous co- Of Pressure polymer when autogenous pressures are used, the conversion must be kept below about 30 percent by weight. Three funs Was Conducted in heavy Walled glass POlYIIl- On the other hand, the composition and homogeneity of erization tubes using the same recipe of Example l above, the, copolymer produced using the constant pressure eXeePt that 110 PefUOfOOetanOiC acid Was employed Afttechnique is independent of conversion and, in general, is el' the tubes Were Changed With 200 Parts 0f Water, 1-0 dependent only on the composition of the feed, a specific Part 0f Potassium PefSUlfale, 04 Part 0f SOCUITl metabfeed of monomer producing a copolymer having the same sulfite and 0.1 pant of ferrous sulfate heptahydrate, the composition as the feed, tubes were evacuated and further charged by ash distillation at liquid nitrogen temperature with 44.6 parts of EXAMPLE 3 ll'chlorouoroethyiene and 554 part? .of tetrauom' Preparation of Copolymer Containing 80 Mol Percent of ethylene correspondmg 'to a charge cqmammg 50 m01 per' 1,1-Chlorouoroet/zylene and 20 Mol Percent of Tetracent of each monomer. After sealing the tubes under uoroethylene vacuum at the temperature of liquid nitrogen, they were rotated end over end in a water bath, the temperature The following emulsion redox polymerization recipe of which was automatically controlled .at 20 C. The was used: polymerizations were conducted under autogenous condi- Parts by tions of pressure. At the end of the period indicated in weight Table 1, the polyrneriziations were stopped and the tubes 40 Water, deionized 200.0 were placed in a liquid nitrogen bath to coagulate the Potassium persulfate 1.() products. The coagulated polymeric products were col- Sodium metabisulte 0.4 lected, washed several times with water and dried to con- Ferrous sulfate 0.1 stant weight in vacuo at a temperature of 35 C. The Cl(CF2-CFC1)3CF2COOH 1.0 results of these three runs are given in 'liable 1, below. 45 Citric acid 0.001

TABLE 1 Composition of Product Run Percent Reaction Nos. Conver- Time Characteristics sion (Hours) Mol Percent Mol Percent CH2=CFC1 CFi--Crz 1 54 24 s2 2s Rubbery. 2 97 23 51 49 Poviefy (very slightly rub- 3 s 0.3 so 2o nubsrl Comparison of the results obtained in these three runs with those obtained in Example 1 above points up several of the advantages of using the constant pressure technique of the invention over the ordinary method of contact polymerizations under autogenous conditions of pressure. The reactivities of 1,1-chloroiluoroethylene and tetraiuoroethylene iare quite different as disclosed in copending application Serial No. 470,194, filed November 22, 1954, the reactivity ratio of 1,1-chlorotiuoroethylene being 2.8-|-0.3 and the reactivity of tetraiiuoroethylene being 0.1-|-0.1. Thus, no feed containing both of these monomers will yield a copolymer of the same compoistion as the feed when the copolymerization is conducted under autogenous pressure or when the monomers are reacted in the liquid phase. In Run No. 2 of Table 1 above, a 51:49 copolymer of 1,1-chlorofluoroethylene:tetrafluoroethylene was obtained from a :50 charge. Although this particular run yielded a copolymer of approximately the same composition as the feed, the product was very A stainless steel polymerization bomb was charged with the following catalyst solutions, freezing the contents in a solid carbon dioxide-acetone bath after each addition:

The bomb was then evacuated and connected to a'steel cylinder equipped with'a pressure gauge and a needle valve located between the bomb and the steel cylinder. The steel cylinder contained a mixture of monomers containing a quantity of 1,1-chlorofluoroethylene and tetrafluoroethylene in liquid phase calculated to provide a feed containing 80 mol percent of l,lchloroliuoroethylene and 20 mol percent of tetratiuoroethylene, or a feed containing 43.9 pants of 1,1-chloroiiuoroethylene and 13.5 parts of tetrafluoroethylene. The needle valve between the steel cylinder and the polymerization bomb was opened and the feed was introduced into the bomb in the gaseous phase at .a rate sufficient to maintain the pressure of polymerization at 50 p.s.i.g. The entire system was rocked at ambient temperature, which was about 25 C. At the end of 17.6 hours the polymerization was short-stopped after only 6.6 parts of feed had been introduced into the bomb. The product in the bomb was in the form of a White latex. The latex was coagulated with a hot dilute sulfuric acid-sodium chloride solution. The coagulated product was collected, thoroughly washed with warm and cold Water, and dried to constant weight in vacuo at a temperature of 35 C. A tacky robbery polymeric product was obtained and was found toV contain 33.18 percent chlorine, or 79 mol percent of combined l,lchlorouoro ethylene and 2l mol percent of combined tetrafluoroethylene.

EXAMPLE 4 Preparation of Copolymer Containing 27 Mol Percent of 1,1-Clzlorofluoroethylene and 73 Mol Percent of Tetra- ]luoroethylene From a 23:77 Molar Feed of Monomers Following the general procedure of Example 3 above, a stainless steel polymerization bomb was charged with the same catalyst solution of Example 3 and further charged with a lmonomer feed containing 14.4 parts of CHgzCFCl and 60 parts of CP2-:CP2 or a monomer feed containing 23 mol percent of CHZICFCl and 77 mol percent of CFFCFZ. The feed was introduced at a rate sufcient to maintain the pressure Within the bomb at 100 p.s.i.g. The bomb was rocked at a temperature of 25 C. (ambient) for a period of 23.3 hours during which time 3'9 parts of monomers Were reacted. The polymeric product was in the form of a fairly firm gel which was ltered, Washed with hot dilute hydrochloric acid and then with Water. Afterdrying to constant weight in vacuo at a temperature of 35 C., 35.7 parts of a powder were obtained, corresponding to a 90 percent conversion of monomers used to copolymer. Upon analysis, the product Was shown to contain 10.0 percent chlorine, corresponding to 27 mol percent of CHFCFCl and 73 mol percent of ClEZICFZ. The powdery copolymer was partly soluble in methyl ethyl ketone and not very soluble in tetrahydrofuran, dimethylformarnide or acetone.

EXAMPLE 5 Preparation of a Copolymer Containing 4 Mol Percent of 1,1-Chlorofluoroethylene and 96 Mol Percent of Tetralztoroethylene From a 2:98 Initial Feed of Monomers Following the general procedure of Example 3 above, a stainless steel polymerization bomb was charged with the same catalyst solution of Example 3, and further charged with .a monomer feed consisting of 2 mol percent of 1,l-chlorolluoroethylene and 98 mol percent of tetrafluoroethylene. The feed was introduced at a rate sutcient to maintain the pressure within the bomb at 100 p.s.i.g. The bomb was rocked at a temperature of 25 C. (ambient) for a period of 23.3 hours during which time 32.1 parts of monomer were reacted. The polymer latex was coagulated, collected, and the coagulated product was treated as described in Example l above. About 32.1 parts of a powder were obtained, the conversion of monomers charged to product being about 100 percent. Analysis for chlorine content showed the copolymer to contain 1.29 percent chlorine, or 4 mol percent of combined 1,1- chloroliuoroethylene and 96 mol percent of combined tetralluoroethylene.

. lo EXAMPLE 6 Preparation of a Copolymer Containing About d0 Mol Percent of Vinylz'dene Fluoride and About 20 Mol Percent of 1,1-Chlorofluoroethylene The following emulsion polymerization recipe was used:

Parts by weight Water, deionized 200.0 Potassium persulfate 1.0 Sodium metabisulte 0.4

Cl(CF2-CFC1)3CF2'COOH '1.0

A stainless steel polymerization bomb was charged With the following catalyst solutions, freezing the contents in a solid carbon dioxide-acetone bath after each addition:

(l) 150 parts of water containing 1.0 part of dissolved Cl (CFZ-CFCl S-CFZCO OH,

(2) 30 parts of water containing 1.0 part of dissolved potassium persulfate, and

(3) 20 parts of waterv containing 0.4 part of dissolved sodium metabisulte.

The bomb was then evacuated and connected to a steel cylinder equipped with a pressure gauge and a needle valve located between the bomb and the steel cylinder. The steel cylinder contained a mixture of monomers consisting of a quantity of vinylidene uoride and 1,1-chlorouoroethylene in the liquid phase, calculated to provide a feed containing mol percent of vinylidene fluoride a-nd 20 mol percent of 1,1-chloro1luoroethylene, or a feed containing 76.1 parts of vinylidene fluoride to 23.9 parts of 1,1-chlorouoroethylene. The needle valve between the steel cylinder and the polymerization bomb was opened and the feed was introduced into the bomb in the gaseous phase at a ra-te suicient to maintain the pressure of polymerization at p.s.i.g. The entire system was rocked at a temperature of 50 C. for a period of 21 hours. The polymer latex was coagulated, collected, washed Iand dried as described in Example 1 above. A solid product was obtained and Was found to contain 8.9 percent fiuorine corresponding to a copolymer containing 82 mol percent of vinylidene fluoride and 18 mol percent of 1,1-chlorouoroethylene.

EXAMPLE 7 Copolymer of ChlorotriYuoroethylene and Vinylidene Fluoride In order to produce a copolymer of chlorotrifluoroethylene and vinylidene fluoride which is to be used as a constituent of a spraying lacquer of excellent grade to be applied as a protective coating on surfaces exposed to strong and corrosive chemicals, it is necessary to control the polymerization conditions so that a copolymer is produced containing between 70 and `80 mol percent chlorotriuoroethylene and having a dilute solution viscosity value ranging between 0.48 and 0.55 centistoke, preferably between 0.05 and 0.53 centistoke.' Such a copolymer should also form a clear solution when 20 parts of it are dissolved in 80 parts of an inexpensive and low boiling organic solvent, such as methyl ethyl ketone, methyl isobutyl ketone, or ethyl butyl ketone. The runs presented in Table 2 below illustrate the use of Various polymerization recipes used to copolymerize CFZICFCI yand CF2=CH2 under autogenous pressure, or in the liquid phase, in the presence of a modier such as chloroform. Results of these runs show that when the polymerization is con-ducted in the liquid phase, it is quite dilicult to control the reactions so as to produce a specific composition possessing the desirable properties mentioned above. Comparisons of the results given in Tables 2 and 3 below will shown that coplymerizing the monomers under a constant pressure which is below the saturation pressure of the monomers is an improved and preferable process i i which can be controlled easily to yield a copolymer having these specific properties.

A series of runs was made using the following polymerization recipe:

The general procedure was the same in each run. Potassium persulfate, sodium metabisulte, ferrous sulfate, and CS-tluorochloro acid were dissolved in aliquots of the 200 parts of water and each solution was charged to a stainless steel polymerization bomb freezing the contents of the bomb in a solid carbon dioxide-acetone bath after each addition. The 7.5 parts of chloroform were then added to the bomb and the bomb was evacuated. A total of 100 parts of a monomer charge, containing CFzICFCl and CF2=CHZ in the mol percent ratio as given to Table 2, were flash distilled into the bomb. The bomb was then closed and rotated end-over-end for the period of time given in Table 2. The polymerization product was coagulatcd by freezing and the coagulated product was collected, Washed, then dried as described in i2 in Table 3 below. The steel cylinders were then disconnected and the bombs were vented to atmospheric pressure. The contents of each bomb were poured into 100 parte of water containing 5 parts of methanol in order to short-stop the polymerization reaction. Each polymer latex was coagulated, collected, Washed and dried as described in Example 1 above. In each run the percentage of monomers which was converted to copolymers was better than 85 percent.

The results are given in the following Table 3.

TABLE 3 Polymer Composition Dilute Run Time Solution Solubility Nos, (Hours) Viscosity Mol Percent Mol Percent (cs) 1 MEK 2 CF2=CFC1 CFz--C n 2 72. 8 27.2 0. 520 Soluble. 1 71.8 28.2 0.505 Do. 3 71.0 29.0 0.505 Do. 3 72.0 28. 0 0. 515 Do.

12 glpcrccnt solution in 3,-dichlerobenzotriiiuoride at a temperature of l.

2 Methyl ethyl ketone.

EXAMPLE 9 The following example illustrates the f-act that conversions up to 95 percent may be obtained of a horno- Example 1. The results of six such runs are given in gefleOuS COPOlYmef having PPIOXIHaCly the Same com- Table 2 position as the monomer feed.

TABLE 2 Composition of Charge, Polymerization Recipe Composition of Product Mol Percent Variables (Parts by Weight) Percent (Infrared Analysis) Dilute Solution in Run Temp., Conversion Mol Percent Solution Methyl No, C. Time Viscosity Ethyl (Hours) (es) 1 Ketonc 2 CFi--CFCl CF2=CH2 KzSzOs NazSzOi C-acid CF2=CFC1 CF2=CH2 75 25 1.00 0.80 15 29.4/6 09 31 0. "40 I s l l 75 25 0. 75 0.60 14 2o. 8/7 69 31 0. 552 n 0151510. 72 28 0. 75 0. 60 15 4. 0/8 G7 33 0. 609 Do. 72 28 0. 75 0.60 16 32. 3/5. 5 66 34 0. 564 Soluble. 72 28 1. 00 0. S0 0.373 2o 26. 7/9 66 34 0. 592 insoluble. 77 23 0.75 0. 60 0. 500 14 12. 0/17. 5 73 27 D0,

1 0.75 percent solution viscosity in a 3,5-dichlerobenzotrifluoride solvent at a temperature of 266 F.

2 20 parts of copolymer in 80 parts of methyl ethyl ketone.

EXAMPLE 8 The following experiment illustrates the advantageous use of the constant pressure technique of copolymerizing CF2=CFC1 and CF2=CH2 at a pressure below the saturation pressure of the monomers.

The following polymerization recipe was employed:

Parts by weight Water, deionized 200.0 Potassium persulfate 1.0 Sodium metabisuliite 0.4 Cl(CF2CFCl)3CF2COOl-I 1.0

A series of stainless steel polymerization bombs was charged with 150 parts of water containing 1.0 part of the CB-fluorochloro acid, parts of water containing 1.0 part of dissolved potassium persulfate, and 20 parts of water containing 0.4 part of dissolved sodium metabisulte. The contents of the bombs were frozen, after each addition, in a bath consisting of solid carbon dioxide and acetone. The bombs were then evacuated and each was connected to a steel cylinder containing 75 mol percent of CFZICFCl and 25 mol percent of CFZIICHZ. The monomer feed was introduced into each bomb at a rate sufficient to maintain polymerization pressure at 141 psig. at a temperature of 75 C. for the periods of time given The following polymerization recipe was employed:

charged with 1000 parts of Water containing 30 parts of potassium persulfate and 5000 parts of water containing 30 parts of dissolved CS-iiuorochloro telomer acid. The autoclave was then evacuated and brought up to atmos` pheric pressure by feeding in a monomer charge consisting of 51.6 parts of CF2=CFC1 `and 8.4 parts of CFzzCl-Iz, corresponding to a feed containing 77 and 23 mol percent of CFFCFCI and CF2=CH2, respectively. The feed was then introduced at a rate sutiicient to maintain the polymerization pressure at 140 p.s.i.g. at a temperature of C. The polymerization was conducted With vigorous mechanical agitation under these conditions for 3.0 hours, after which time approximately 3900 parts of monomers had been charged. White latex was obtained having a high solids content with very little polymer formation on the walls of the autoclave. The

latex was discharged and coagulated by freezing. The coagulated latex was washed thoroughly with cold and hot Water, collected and dried to constant weight in vacuo at a temperature of 35 C. About 3700 parts of a tine white powder were obtained; the conversion of monomers charged-to monomers reacted .to produce the copolymer was about 95 percent.

Infrared analysis of the :product showed it to be very homogeneous and to contain 73.11101 percent of combined chlorotriiluoroethylene and 27 mol percent of combined vinylidene fluoride. The product had a 0.75 percent solution viscosity value, as determined in a =35dichlorobenzotrilluoride solvent at 266 F., of 0.515 centistoke. The product was pressed to form a very clear and colorless sheet. The product was soluble in methyl ethyl ketone, methyl isobutyl ketone and ethyl butyl ketone.

EXAMPLE Preparntion of a 45 :55 Mol Percent CFzr-CFCZ CF2=CH2 Copolymer From a 45:55 Mol Percent Monomer Feed This example and the following Example 11 are illustrative of the fact that reactivity ratios need not be considered when copolymerlizing two monomers of different reactivities, according to the process of the invention.

A stainless steel polymerization bomb was charged with the same polymerization recipe and vin the same manner as described in Example 3 above. A monomer feed consisting of 59.8 parts of CF2=CFC1 and 40.2 parts of CFFCHZ, equivalent to a feed consisting of 45 mol percent of CFFCFCI and 55 mol percent of CF2=CH2, was introduced into the bomb at ya rate sutlicient to maintain the polymerization pressure at 100 p.s.i.g. at a temperature of 25 C. After rocking the system for 4 hours under these conditions, 54.4 parts of monomers had been charged. The latex was worked up in the same manner as described in Example 1 above and 46.0 parts of a rubbery product was obtained, the conversion being 93 percent. Analysis for fluorine and chlorine content showed the product to containv 45 and 55 mol percent of combined chlorotriuoroethylene and vinylidene fluoride, respectively.`

EXAMPLE 11 The following polymerization recipe was employed:

I Parts by weight Water, deionized 200.01 Potassium persulfate 1.0 Sodium metabisulte 0.4

A stainless steel polymerization bomb was charged with 100 parts of water containing 1.0 part of dissolved potassium persulfate, and 100 parts of water containing 0.4 part of sodium metabisulte, freezing the contents of the bomb after each addition. The bomb was then charged in the `manner described in Example 1 above with a monomer feed containing 12.6 parts of CFZICFCI and 62.4 parts of CF2=CH2 or a feed containing 10 and 90 mol percent of CF2=CFC1 and CF2=CH2, respectively. The feed was introduced at la rate suicient to maintain the polymerization pressure at 140 p.s.i.g. at a temperature of 50 C. The entire system was rocked under these conditions for a period of 6.5 hours after which time the polymer latex was treated 'as described in Example 1, tabove. A powdery product was obtained in an 86 percent conversion of monomers charged (18.7 parts) to copolymer product (16.0 parts). Chlorine and fluorine analysis showed the product to contain' 12 and 88 mol percent of combined chlorotriliuoroethylene `and vinylidene fluoride, respectively.

Vinyldene Fluoride 'at a Pressure Below the Saturation Pressure of the Mono/ners A stainless steel polymerization bomb was charged with `the same polymerization catalyst `system as employed in Example 3 above except that 0.002 part ofcitric acid Was used instead of `01001 part. The bomb was evacuated and charged with a monomer feed consisting of 25.7 parts of CFZICFZ `and 49.3 parts -of iCFE-TCH? ora feed containing 25 and 75 mol percent of CP2-*JCE and CF2=CH2, respectively. The feed was introduced at a rate sufcient 'to maintain the polymerization pressure 'at 310 p.s.i.g. at 25 C. for a period of 17 hours after which time 54.7 parts of monomers had been charged to the bomb. The latex was worked up as described in Example 1 above. A powdery product (52.0 parts) was obtained in 95 ,percent conversion and was found to .contain 34 mol percent of combined tetrafluoroethylene 'and 66 ymol percent of combined vinylidene fluoride.

EXAMPLEv 13 This example illustrates the 4homopolymerization of a ilumine-containing monomer, such as vinylidene fluoride, yat a pressure "below 'the saturation pressure of the monomer.

Astainless steel polymerization -bomb was charged with the same polymerization recipe and in `the same manner as described in Example 11 above, and further charged in the Vsame manner described in Example 1 above with vinylidene fluoride in the vapor phase at a rate sufficient to maintain the polymerization pressure in the bomb at i-p.s.i.g. at a temperature of 50 C. The entire system was rocked under these conditions for a period of 2 hours. All of the polymer product Was easily collected by filtration, andthe filtered powdery material was washed thoroughlywith water Vand dried `to constant weight in vacuo at a temperature of 35 C. The powdery polymeric product contained 59.04 percent fluorine (theoretical fluorine lcontent is 59.38 percent) and was obtained in an 80 percent conversion.

A good yield of polyvinylidene fluoride was also obtained using the Vrecipe of Example 12 above and feeding vinylidene fluoride into thepolymerization bomb at a rate suicient to maintain the polymerization pressure at y400 p.s.i.g. at a temperature of 25 C. for 16.5 hours. f

EXAMPLE 14 Homopolymerz'zatz'on of Chlorotrz'uoroethylene at a Pressure Below the Saturation Pressure ofthe M Onomer The following polymerization recipe was used:

Parts by `Weight Water, deionized 300.0 Potassium persulfate 2.4 `C1(CF2CFC1)3CF2COOK 2.4 Sodium orthophosphate (bulfer) 2.4

A stainless steel polymerization bomb was charged with the following ingredients, freezing the contents of the bomb in a solid carbon dioxide-acetone bath after each addition:

(1) 95 parts of aneutral aqueous solution containing 2.4 parts of the potassium salt of Cs-fluorochloro telomer acid, and

(2) 45 parts of an aqueous solution containing 2.4 parts of potassium persulfate.

The pH of the mixture was then adjusted to 8.5 by the addition of potassium hydroxide, and then parts of water containing 2.4 parts of dissolved sodium orthophosphate (Na2HPO4-l2I-I2O) were added. The bomb Was then evacuated and a feed of chlorotrifluoroethylene was introduced at a rate sufficient to maintain the polymerization pressure at 70 p.s.i.g. The polymerization was conducted for 19 hours at 70 p.s.i.g. and at a temperature of about 25 C. The final pH of the system was,7.8. The polymer latex contained a high solids content and was coagulated by freezing. The coagulated product was easily removed from the bomb and was washed thoroughly with cold and then warm water and dried to constant weight at a temperature of 190 C. The product was obtained in about a 70 percent conversion, and had a dilute solution viscosity value of 0.924 centistoke which is equivalent to an N.S.T. of 270 C.

EXAMPLE The following polymerization recipe was used:

Parts by Weight Water 200.0 Potassium persulfate 1.0 C1(CF2CFC1)3CF2COOH 10.0

A polymerization tube was charged with 50 parts of water containing 1.0 part of potassium persulfate and 150 parts of water containing 10 parts of dissolved C8- fluorochloro telomer acid. The tube was then evacuated and a monomer charge consisting of 58.0 parts of chloroprene and 42.0 parts of vinylidene fluoride, corresponding to a feed containing 50 mol percent of each monomer, was fed -to the tube at a rate sutlicient to maintain a constant polymerization pressure at 140 p.s.i.g. at a temperature of 40 C. The entire system was rotated endover-end in a water bath for a. period of 19 hours, at the end of which the copolymer latex was coagulated with a sodium chloride-sulfuric acid solution. The coagulated product was washed and dried at constant weight in vacuo at a temperature of 35 C.

The product was a rubbery copolymer obtained in a yield of 16 parts by weight, and chlorine analysis of the product showed it to contain 35.48 percent by weight chlorine corresponding to a copolymer containing 15 mol percent of vinylidene liuoride and 85 mol percent of chlooprene. Fluorine analysis ofthe product showed it to contain 8.01 percent of iiuorine corresponding to a copolymer containing 17.5 mol percent of vinylidene iuoride and 82.5 mol percent of chloroprene.

In contrast to the results obtained in this examplel when a monomer mixture containing 50 molpercent of vinylidene fluoride and 50 mol percent of chloroprene was copolymerized in a cumene hydroperoxide redox emulsion system at a temperture of C. for 16 hours under autogenous pressure, only 8 mol percent of vinylidene fluoride was incorporated into the copolymer product.

EXAMPLE 16 Using the same polymerization recipe and charging procedure of Example 14 above, triiiuoroethylene is polymerized at a constant pressure of 200 p.s.i.g. at a temperature of C. for a period of 20 hours. The product is worked up as before, and the yield is about parts of triuoroethylene homopolymer.

EXAMPLE 17 The same polymerization recipe and charging procedure used in Example 14 above is used .to polymerize tetrauoroethylene at a constant pressure of 300 p.s.i.g. and a temperature of 25 C. for a period of 6 hours. The product is worked up before, and the yield is about parts of tetrauoroethylene homopolymer.

EXAMPLE 18 Using the same polymerization recipe and charging procedure of Example 14 above, 1,lch1orofluoroethylene is polymerized at a constant pressure of 40 p.s.i.g. at a temperature or' 25 C. for a period of 20 hours. The product is worked up as before, and the yield is about 50 parts of 1,1-ch1orot1uoroetl1ylene homopolymer.

CTI

i@ EXAMPLE 19 The same polymerization recipe and charging procedure of Example 14 above is used to copolymerize a monomer mixture containing 30 mol percent of tetrauoroethylene and mol percent of butadiene at a constant pressure of p.s.i.g. and a temperature of 50 C. for a period of. l0 hours. The product is worked up as before and contains between about 20 and 30 mol percent of combined tetrailuoroethylene.

EXAMPLE 20 Copolymerzation at a Pressure Below the Saturation Pressure of One Monomer and Above the Saturation Pressure of the Other The polymerization recipe and charging procedure of Example 14 above is used to copolymerize a charge containing 50 mol percent of chlorotrifluoroethylene and 50 mol percent of styrene at a constant pressure of 40 p.s.i.g. and a temperature of 50l C. for a period of 24 hours. The product was worked upas before and contains about 40 mol percent of combined chlorotriuoroethylene.

It will be obvious to those skilled in the art that many modifications may be made within the scope of the present invention without departing from the spirit thereof, and the invention includes all such modifications.

This application is a continuation of Serial No. 475,385, tiled December 15, 1954.

I claim:

l. A continuous copolymerization process comprising continuously charging a mixture of (l) an ethylenically unsaturated uoroolenic monomer having not more than about 8 carbon atoms and having at least one lluorine atom attached to a carbon atom of the ethylenically unsaturated monomer nucleus, and (2) a different ethylenically unsaturated copolymerizable monomer having not more than `about 8 carbon .atoms into the polymerization zone at a rate suflicient to maintain a constant pressure in the polymerization zone, maintaining said polymerization zone at a preselected temperature between about 0 C. and -about 100 C., .the pressure in the zone being below the saturation pressure of both monomers at said preselected temperature, introducing an aqueous free radical catalyst solution into said polymerization zone, copolymerizin-g the monomers charged to said polymerization zone, Iand removing the copolymer product from said polymerization zone.

2. A copolymerization process according to claim 1 in which the monomers are recirculated from the upper portion of the polymerization zone to the lower portion thereof.

3. A copolymerization process according to claim 1 in which the monomers are 1,1-chlorouoroethylene and tetraiiuoroethylene.

4. A copolymerization :process according to claim 1 in which the monomers are chlorotriiluoroethylene and vinyli-dene uoride.

5. A copolymerization process according to claim l in which the monomers are tetnatluoroethylene and vinylidene fluoride.

6. A copolymerization process according to claim 1 in which the monomers are chlorotritiuloroethylene and styrene.

7. A copolymerization process according to claim l in which the monomers are chloroprene and vinylidene uode.

References Cited in the le of this patent UNlTED STATES PATENTS 2,393,967 Brubaker Feb. 5, 1946 2,559,752 Berry July l0, 1951 2,904,409 nomad Sept. 15, 1959 UNITED STATES PATENT OFFICE CERTIFICATE 0F CORRECTION Patent No 3 ,163,628 December 29, 1964 Archibald N. Bolstad It is hereby certified thaterror appears n the above numbered patent requiring correction and that the said. Letters Patent should read as corrected below.

Column 7, TABLE l, fifth column, line 1 thereof, for "28" read 18 column 15, line 66, after "up" insert as line 73, for "Z0 hours" read 6 hours Signed and sealed this 13th day of July 1965.,

(SEAL) Attest:

ERNEST W. SWIDER EDWARD J. BRENNER Attesting Officer Commissioner of Patents 

1. A CONTINUOUS COPOLYMERIZATION PROCESS COMPRISING CONTINUOUSLY CHARGING A MIXTURE OF (1) AN ETHYLENICALLY UNSATURATED FLUOROOLEFINIC MONOMER HAVING NOT MORE THAN ABOUT 8 CARBON ATOMS AND HAVING AT LEAST ONE FLUORINE ATOM ATTACHED TO A CARBON ATOM OF THE ETHYLENICALLY UNSATURATED MONOMER NUCLEUS, AND (2) A DIFFERENT ETHYLENICALLY UNSATURATED COPOLYMERIZABLE MONOMER HAVING NOT MORE THAN ABOUT 8 CARBON ATOMS INTO THE POLYMERIZATION ZONE AT A RATE SUFFICIENT TO MAINTAIN A CONSTANT PRESSURE 